Toronto publisher Wm Collins Sons & Co. Canada Ltd published 459 books between 1942 and 1952 in their paperback series White Circle Pocket Library. From 1952 until 1990, when Wm Collins merged with Harper and Row, other series were published. Here is an example from one of them - Collins Crime. I don't know how many books were published in this series.
Further on are examples of White Circle Pocket Library crime.